ColorPaletteGlitch with Modified FastLED example

#include <FastLED.h>

#define LED_PIN     23
#define NUM_LEDS    300
#define BRIGHTNESS  255
#define LED_TYPE    WS2811
#define COLOR_ORDER GRB
CRGB leds[NUM_LEDS];

#define UPDATES_PER_SECOND 50

// This example shows several ways to set up and use 'palettes' of colors
// with FastLED.
//
// These compact palettes provide an easy way to re-colorize your
// animation on the fly, quickly, easily, and with low overhead.
//
// USING palettes is MUCH simpler in practice than in theory, so first just
// run this sketch, and watch the pretty lights as you then read through
// the code.  Although this sketch has eight (or more) different color schemes,
// the entire sketch compiles down to about 6.5K on AVR.
//
// FastLED provides a few pre-configured color palettes, and makes it
// extremely easy to make up your own color schemes with palettes.
//
// Some notes on the more abstract 'theory and practice' of
// FastLED compact palettes are at the bottom of this file.



CRGBPalette16 currentPalette;
TBlendType    currentBlending;

extern CRGBPalette16 myWhitePalette;
extern const TProgmemPalette16 myWhitePalette_p PROGMEM;


void setup() {
  delay( 3000 ); // power-up safety delay
  FastLED.addLeds<LED_TYPE, LED_PIN, COLOR_ORDER>(leds, NUM_LEDS).setCorrection( TypicalLEDStrip );
  FastLED.setBrightness(  BRIGHTNESS );

  currentPalette = CloudColors_p;
  currentBlending = NOBLEND;
}


void loop()
{
  ChangePalettePeriodically();

  static uint8_t startIndex = 0;
  startIndex = startIndex + 1; /* motion speed */

  FillLEDsFromPaletteColors( startIndex);

  FastLED.show();
  FastLED.delay(1000 / UPDATES_PER_SECOND);
}

void FillLEDsFromPaletteColors( uint8_t colorIndex)
{
  uint8_t brightness = 255;

//  for( int i = 0; i < NUM_LEDS; i++) {
//    leds[i] = ColorFromPalette( currentPalette, colorIndex, brightness, currentBlending);
//    colorIndex += 3;

  for( int i = 0; i <= NUM_LEDS/2; i++) {
    leds[i] = ColorFromPalette( currentPalette, colorIndex, brightness, currentBlending);
    leds[NUM_LEDS-i] = ColorFromPalette( currentPalette, colorIndex, brightness, currentBlending);
    colorIndex += 3;

  }
}


// There are several different palettes of colors demonstrated here.
//
// FastLED provides several 'preset' palettes: RainbowColors_p, RainbowStripeColors_p,
// OceanColors_p, CloudColors_p, LavaColors_p, ForestColors_p, and PartyColors_p.
//
// Additionally, you can manually define your own color palettes, or you can write
// code that creates color palettes on the fly.  All are shown here.

void ChangePalettePeriodically()
{
  uint8_t secondHand = (millis() / 1000) % 60;
  static uint8_t lastSecond = 99;

  if( lastSecond != secondHand) {
    lastSecond = secondHand;
    if( secondHand == 0)   { currentPalette = CloudColors_p;           currentBlending = BLEND; }
    if( secondHand == 20)  { SetupRedAndGreenPalette();                currentBlending = NOBLEND; }
    if( secondHand == 40)  { currentPalette = myWhitePalette_p;        currentBlending = BLEND; }
  }
}

// This function fills the palette with totally random colors.
void SetupTotallyRandomPalette()
{
  for( int i = 0; i < 16; i++) {
    currentPalette[i] = CHSV( random8(), 255, random8());
  }
}

// This function sets up a palette of black and white stripes,
// using code.  Since the palette is effectively an array of
// sixteen CRGB colors, the various fill_* functions can be used
// to set them up.
void SetupBlackAndWhiteStripedPalette()
{
  // 'black out' all 16 palette entries...
  fill_solid( currentPalette, 16, CRGB::Black);
  // and set every fourth one to white.
  currentPalette[0] = CRGB::White;
  currentPalette[4] = CRGB::White;
  currentPalette[8] = CRGB::White;
  currentPalette[12] = CRGB::White;

}

// This function sets up a palette of purple and green stripes.
void SetupRedAndGreenPalette()
{
  CRGB red = CHSV( HUE_RED, 255, 255);
  CRGB green  = CHSV( HUE_GREEN, 255, 255);
  CRGB black  = CRGB::Black;

  currentPalette = CRGBPalette16(
    green,  green,  red,  red,
    green, green, red,  red,
    green,  green,  red,  red,
    green, green, red,  red );
}


// This example shows how to set up a static color palette
// which is stored in PROGMEM (flash), which is almost always more
// plentiful than RAM.  A static PROGMEM palette like this
// takes up 64 bytes of flash.
const TProgmemPalette16 myWhitePalette_p PROGMEM =
{
  CRGB::White,
  CRGB::White, // 'white' is too bright compared to red and blue
  CRGB::White,
  CRGB::White,

  CRGB::Gray,
  CRGB::Gray,
  CRGB::Gray,
  CRGB::Gray,

  CRGB::White,
  CRGB::White, // 'white' is too bright compared to red and blue
  CRGB::White,
  CRGB::White,

  CRGB::Gray,
  CRGB::Gray,
  CRGB::Gray,
  CRGB::Gray
};



// Additionl notes on FastLED compact palettes:
//
// Normally, in computer graphics, the palette (or "color lookup table")
// has 256 entries, each containing a specific 24-bit RGB color.  You can then
// index into the color palette using a simple 8-bit (one byte) value.
// A 256-entry color palette takes up 768 bytes of RAM, which on Arduino
// is quite possibly "too many" bytes.
//
// FastLED does offer traditional 256-element palettes, for setups that
// can afford the 768-byte cost in RAM.
//
// However, FastLED also offers a compact alternative.  FastLED offers
// palettes that store 16 distinct entries, but can be accessed AS IF
// they actually have 256 entries; this is accomplished by interpolating
// between the 16 explicit entries to create fifteen intermediate palette
// entries between each pair.
//
// So for example, if you set the first two explicit entries of a compact
// palette to Green (0,255,0) and Blue (0,0,255), and then retrieved
// the first sixteen entries from the virtual palette (of 256), you'd get
// Green, followed by a smooth gradient from green-to-blue, and then Blue.